Recently, variable resistance type memories have been studied as memories replacing flash memories which approach the limit of reduction of flash memory size. As one example of these studies, phase change memories in which chalcogenide materials are used as storage materials have been actively studied. A memory structure of the phase change memory is a structure in which the storage material is sandwiched by metal electrodes. The phase change memory is a variable resistance type memory that stores information by using a phenomenon in which the storage material between the electrodes has different resistance states.
The phase change memory stores information by using a phenomenon in which resistivities of the phase change materials such as Ge2Sb2Te5 are different in an amorphous state and a crystal state. The phase change memory has higher resistance in the amorphous state and has lower resistance in the crystal state. Therefore, read is performed by applying voltage difference across an element, measuring current flown through the element and determining whether the resistance state of the element is high or low.
The phase change memory programs data by changing electric resistance of a phase change film in different states by Joule heat generated by current. A reset operation, in other words, an operation to change into the amorphous state being high resistance is performed by melting the phase change material by applying large current for a short time, and thereafter by quenching by rapid decrease in the current. On the other hand, a set operation, in other words, an operation to change into the crystal state being low resistance is performed by applying sufficient current to maintain crystallization temperature of the phase change material for a long period. This phase change memory is suitable for reduction of memory size in principle because, when the reduction of phase change memory size proceeds, required current to change a state of a phase change film becomes lower. Therefore, the phase change memory has been actively studied.
As a method for integrating the memory using these variable resistance type elements, Patent Literature 1 discloses constitution in which, in stacked structure formed by alternately stacking a plurality of gate electrode materials and insulator films, a plurality of through holes that pass through the entire layers is collectively patterned at the same time, and a gate insulator film, a channel layer, and the phase change film are formed and patterned on the inside of the through holes.
A literature related to this invention includes Nonpatent Literature 1. Nonpatent Literature 1 discloses an NAND-type flash memory having a similar structure to Patent Literature 1.